When you'd like to invite someone to work on a session with you, you can do so in a number of ways.
However, adding a collaborator to a session compared to adding a member to your workspace will result in different benefits, explained here:
Inviting a collaborator to your session:
The user will be able to access and edit that one session you've invited them to
They will not see any other session you have created in your workspace
The invited user will have Pro rights in the session you invited them to (e.g. they'll be able to invite other users to that session too, and export it in formats they otherwise wouldn't have access to)
However the user will not have Pro rights in their account - they can only create up to 3 sessions, and only use the Free features on those limited sessions
Inviting session collaborators is available on the Pro and Business subscriptions, and not on the Free or Individual plans.
Adding a user as a member of your workspace:
The member will be able to access and view every session in the workspace you've added them to
If you make that person an 'Admin' of your workspace, they will automatically have editor rights to every session in your workspace
As a paid workspace member, they will also be able to create an unlimited number of their own session plans, as well as access all the features of the Pro or Business plan, depending on which subscription tier you upgraded to
You can add users to your workspace, even if you are on the Free plan. This means that the members can view all the session plans in the workspace, but they won't be able to edit them